Just 35% of the timber cut down in forests is used in mass timber projects, with the remaining “slash” – including branches, twigs, roots and bark re-releasing biogenic carbon into the atmosphere, which has, until now, been unaccounted for in life cycle assessments of timber buildings.
However, that could change thanks to a new Mass Timber Carbon Calculator developed by one of the world’s largest architectural practices, Cogan, which addresses the elephant in the room – the assumption that mass timber is carbon neutral due to carbon capture during a tree’s life.
“Approximately 20% of a building’s total energy usage over its lifetime is determined long before it is even built and occupied,” according to Varun Kohli, director of Corgan’s sustainability practice—Echo. “Our tool provides a methodology to help provide the industry with additional data for a more informed decision for Mass Timber projects, especially as the global demand for wood products continues to multiply.”
Exploring three types of common slash methods—site composting, pile burning, and mastication—and seven species used in US projects (Alaska Yellow Cedar, Douglas Fir, Hemlock Fir, Ponderosa Pine, Southern Yellow Pine, Spruce Pine Fir, and Western Red Cedar), the tool fully accounts for harvesting, processing, fabrication and transportation to the building site.
And to illustrate its practical application, Corgan conducted a case study on a theoretical 216,000-square-foot, six-story office building with mass timber structural elements: “This study found that even with the worst-case scenario for slash management, mass timber accounts for lower embodied carbon values than concrete or steel structures,” Corgan said.
According to Mahdi Afkhami, a design researcher at Corgan’s in-house research group, Hugo, the tool will empower architects to confidently present mass timber’s biogenic carbon value: “Our research is the next step in fostering industry collaboration. We hope this collective effort will improve carbon accounting practices and promote more sustainable construction processes.”
The byproduct of a white paper, Understanding Real CO2e Emissions in Mass Timber Production, Corgan’s Echo and Hugo teams show that the differences between the current biogenic carbon and the below-ground and slash-released carbon can account for up to 30-34% of structural columns, flooring, and framing: “This methodology provides an estimation of omitted GHG emissions and brings us closer to real embodied carbon values in mass timber.”
- For more information, visit Corgan’s MTCalculator.
